The invention is suited for control of the voltage level of load signals UL from transmitters in a data transmitting system sending data in low-voltage network. The aim is to keep the load signal as to its voltage level as constant as possible in the transmitter mains connection that is independent of net impedance, which impedance can sometimes be quite low and thus tending to attenuate the load signal to a degree unfit for use with respect to reliable communication. Usually, by low-voltage a net of 230 V 50 Hz or some other low-voltage net is referred to.